1. Field of the Invention
This invention relates to a toner scraper which is used for scraping off a toner adhering to a roll or belt-like rotation body. Such a rotation body is disposed as a component of a developing device which develops an electrostatic latent image formed on a latent image holder with using the toner.
2. Description of the Related Art
As an example of a developing device which develops an electrostatic latent image formed on a latent image holder such as a photosensitive drum with using a toner, a one-component developing device is known (for example, Japanese Patent Unexamined Publications Nos. SHO47-13088, and SHO62-251771). In such a one-component developing device, as shown in FIG. 7, a toner 5 supplied to a rotating roll-like toner carrier 41 is formed into a thin layer by a layer forming member 6 which is compressedly contacted with the toner carrier 41. Thereafter, the toner layer is transported to a development area which opposes a latent image holder 7, and the toner is caused to adhere to a latent image 8 formed on the latent image holder 7, thereby developing the latent image.
In such a developing device, generally, it is important to stably supply a toner to the toner carrier, to stably form a layer of the toner supplied to the carrier, and to cause the toner in the form of a layer to adhere with fidelity to the electrostatic latent image. Also, it is important to prevent the image hysteresis (development ghost) phenomenon from occurring on the toner carrier.
As shown in FIG. 7, therefore, Japanese Patent Unexamined Publication No. HEI4-100075 discloses developing device in which applying a bias voltage from a power source 10 across the toner carrier 41 and a roll-like toner supply member 42 for supplying a toner to the toner carrier 41, so that the toner is stably supplied to the toner carrier. Further, when an excess amount of a toner adheres to the toner supply member 42, the ability of supplying the toner to the carrier is lowered. In order to prevent the toner supply ability from being lowered, Japanese Patent Unexamined Publication No. HEI4-37778 discloses a developing device which is provided with a toner scraper 100 that is contacted with the surface of the toner supply member 42.
Japanese Patent Unexamined Publication No. SHO60-002967 discloses to use a roll-like layer forming member which rotates while contacting with the toner carrier in order to stably form a thin layer of a toner on the toner carrier. Also when an excess amount of a toner adheres to the surface of the roll-like layer forming member, it is impossible to stably conduct the layer formation. Accordingly, the developing device is provided with a toner scraper which is contacted with the surface of the roll-like layer forming member.
Moreover, Japanese Patent Unexamined Publication No. SHO62-251771 discloses a toner scraper which is directly contacted with the toner carrier in order to prevent the image hysteresis phenomenon from occurring. Japanese Patent Examined Publication No. HEI1-49945 discloses a toner peeling roll which is rotatively contacted with the toner carrier and for disposing a toner scraper for removing a toner adhering to the peeling roll.
The image hysteresis is a phenomenon in which the thickness and toner electrification of a toner thin layer in an area where is previously used in the development (developing area) are different from those in another area where is not previously used in the development (nondeveloping area), and, when developments of the same image are continuously conducted and a development of a different image is then conducted, the development of the different image is affected by the previous developments (that is, the amount of a toner on the area of the toner carrier which corresponds to the nondeveloping area of the previous development is smaller that on the area which corresponds to the developing area of the previous development). As a result of the image hysteresis, in an obtained image, the density of the image portion corresponding to the nondeveloping area of the previous development is different from that of the image portion corresponding to the developing area (the image portion corresponding to the nondeveloping area is lower than that of the image portion corresponding to the developing area), thereby making the image density uneven.
In such a one-component developing device, or the like, a known toner scraper for scraping off a toner from the surface of a rotation body such as a toner carrier, a toner supply roll, a roll-like layer forming member, or a peeling roll has a configuration such as shown in FIGS. 8(a) or (b). In the configuration shown in FIG. 8(a), an elastic member 101 such as a rubber plate, a stainless steel plate, or a polyester film is supported and fixed at one end portion, and under this state the elastic member is contacted with the surface of a rotation body. In the configuration shown in FIG. 8(b), the elastic member 101 is attached in a rigid holder 102 for fixation and support in such a manner that the front end of the elastic member protrudes from the holder. However, such a known toner scraper has the following problems.
In order to enhance the effect of scraping off a toner, generally, the front edge portion of a scraper is contacted with the surface of a rotation body with a predetermined inclination angle. However, it is difficult that the toner scraper is uniformly contacted with the rotation body along the longitudinal direction of the rotation body.
In the realization of the uniform contact, the linearity of the edge portion of the toner scraper along the longitudinal direction, the working accuracy of the edge portion, and the positional accuracy of the contact between the edge portion and the rotation body play important roles. However, it is difficult for such a conventional toner scraper to accomplish these requirements. If a toner scraper is constructed or installed in a high accuracy, the cost of the toner scraper is increased. Accordingly, a toner scraper made of an elastic material is usually contacted with the whole area of the rotation body at a relatively high contact pressure (about 60 gf/cm or higher), so that the uniform contact is attained. In a toner scraper composed of a rubber member, particularly, it is often that the forming accuracy of the edge portion is difficult to improve, and the linearity thereof is liable to be impaired during a process of attaching the rubber member. Therefore, the contact pressure of a toner scraper composed of a rubber member must be set to be a higher value (about 80 gf/cm or higher) than that of a toner scraper composed of a member of another kind.
However, a high contact pressure produces further problems as described below.
If a plate spring member made of a metal such as a stainless steel plate is used as a toner scraper, a high stress concentrates at an edge portion contacting with a rotation body. In this case, therefore, the surface of the rotation body contacting with the edge portion is liable to be damaged. Moreover, since a toner is deteriorated in a short period by a stress which is applied on the toner during the scraping process, the scraped toner cannot be returned to the developer to be reused. In addition, if a film member of a plastic such as polyester is used as a toner scraper, the durability of the film member itself is low. In this case, therefore, the toner scraper is extremely abraded as a result of a long period use to be difficult to be used. Also in the case of a rubber member, since the front edge portion is contacted with the rotation body at a high pressure, the frictional resistance is high so that the driving torque of the rotation body is increased. When the toner scraper is used for a long period, this high frictional resistance causes the toner scraper to be easily abraded, thereby deteriorating the toner.
Moreover, in the case where a toner which is scraped off by a toner scraper under such a high contact pressure is returned to the developer to be reused, particularly when the toner is a polyester toner having a low glass transition temperature, the toner scraper applies a stress to the toner to deteriorate it uniformly in a short period use. This arises a problem in that the layer forming member cannot stably conduct the layer formation and hence a layer disturbance is generated.